1. Field of the Invention
The present invention relates to a substrate processing apparatus having a polishing unit for polishing a periphery of a substrate, and more particularly to a substrate processing apparatus having a mechanism for inspecting a polished surface.
2. Description of the Related Art
There is an increasing demand for a high throughput in a semiconductor-device fabrication process. Under such a demand, there has recently been developed a polishing apparatus having multiple polishing modules arranged so as to surround a substrate. This type of polishing apparatus realizes a high throughput by operating the multiple polishing modules simultaneously to polish a periphery of the rotating substrate. Generally, the polishing apparatus has a module for detecting an end point of polishing of a substrate. Examples of such a polishing-end-point detection module include a so-called in-situ polishing-end-point detection module which is incorporated in the polishing apparatus.
The polishing-end-point detection module of in-situ type is generally designed to monitor a film on the periphery of the substrate while the polishing modules are polishing the periphery of the substrate, and determine the polishing end point based on a time when the film is removed. Therefore, it is necessary to arrange the polishing-end-point detection module next to the polishing modules. However, since the plural polishing modules access the substrate during polishing of the substrate, there is no space for the polishing-end-point detection module to access the substrate. Moreover, in view of the fact that the high-throughput polishing apparatus polishes each substrate in several seconds, it becomes meaningless to detect the polishing end point during polishing.
Further, a polishing liquid (typically pure water), which is supplied to the substrate during polishing, can hinder the polishing-end-point detecting operation of the polishing-end-point detection module. There is an in-situ type which uses a transparent tape through which the periphery of the substrate is monitored, with a view to avoiding such an influence of the polishing liquid. In this type of module, the transparent tape is brought into contact with the periphery of the substrate while advancing the transparent tape, and polishing of the periphery of the substrate is monitored from the back of the transparent tape. However, this solution requires a highly-transparent tape and thus entails an increased cost.